After a part of a bone is surgically removed because of disease such as malign tumor or osteomyelitis, a method of transplanting (grafting) an artificial bone formed from a metal instead of the removed bone has been generally adopted. The transplantation (graft) of the artificial bone is made, for example, by providing a cavity in a natural bone for receiving the artificial bone after removing a part of the natural bone, then filling the cavity with a bonding agent, putting the artificial bone into the bonding agent and curing the bonding agent to close the gaps between the natural bone and the artificial bone and adhere them to each other. As the bonding agent, there has been conventionally employed a mixture of methyl methacrylate (referred to hereinafter as "MMA") and a polymerization initiator such as benzoyl peroxide (referred to hereinafter as "BPO") or a mixture of peroxide and a tertiary amine. For curing the bonding agent, the bonding agent is subjected to polymerization reaction at normal temperatures.
However, the cured product shows poor adhesivity to a natural bone, and moreover the curing reaction of MMA is an exothermic reaction, so that the organization of the bone may be denatured owing to the generated heat during the curing reaction of MMA in the case that the reaction is performed at a high speed.
In more detail, when the polymerization reaction of MMA is performed using such a conventional polymerization initiator as a mixture of BPO and amine, the reaction proceeds rapidly to release a reaction heat in a short period of time, so as to temporarily make the temperature of MMA (or cured product of MMA) relatively high. Hence, the organization of the natural bone in contact with the cured product of MMA might be easily denatured.
Further, the cured product of MMA has a low affinity with an organism (i.e., living body), and any substantial adhesive force is not produced between not only the cured product and the artificial bone but also the cured product and the natural bone, so that looseness is brought about with time on each interface therebetween.
For coping with the above-described drawbacks, there has been proposed a method of making the artificial bone itself have a affinity with a natural bone and bonding the surface of the artificial bone to the natural bone grown with time to unite them with each other. That is, the surface of the artificial bone is covered with calcium phosphate such as hydroxyapatite (referred to hereinafter as "HAP") having high affinity with a natural bone to unite the artificial bone to a newborn bone grown with time through calcium phosphate, so as to firmly fix the artificial bone on the natural bone.
However, the method for fixing the artificial bone on the natural bone depending upon a natural healing power of a living body requires a long period of time for growth of a newborn bone, and therefore the affected part must be fixed for that long period of time. The fixing of the affected part for a long time brings about adverse side effect such as reduction of muscular strength or kinetic functions of joints, and in order to recover the reduced functions, rehabilitation of a long period of time is necessary. Such rehabilitation makes the burden too heavy for the patient. Especially for aged persons, such burden is a severe problem because the growth of a newborn bone is slow and a very long time is required for curing the affected part.
Furthermore, since calcium phosphate itself does not have any adhesive force to the artificial bone, it is very important to allow to firmly adhere calcium phosphate to the artificial bone and to cover the artificial bone with calcium phosphate. In the prior arts, the adhesion between the artificial bone and calcium phosphate is insufficient, and various problems still remain accompanied by the insufficient adhesion.
In more detail, for making the artificial bone or artificial tooth root covered with calcium phosphate exhibit the desired functions, it is required that calcium phosphate is firmly adhered to a metal that is a main structural body of the artificial bone or the artificial tooth root. However, most of the artificial bones or artificial tooth roots covered with calcium phosphate are insufficient in this viewpoint. Further, in order to give calcium phosphate a sufficient affinity with organism, it is also required that calcium phosphate has its crystalline structure almost the same as that of the rigid organization of a living body (i.e., natural bone), and that the metal is covered with calcium phosphate of high purity.
For satisfying those requirements, a complex process for preparing the artificial bone or the artificial tooth root is needed, and besides, calcium phosphate is necessarily treated at a high temperature in the process for the preparation. However, even in the case of producing an artificial bone or an artificial tooth root in consideration of the above-mentioned viewpoints, there can be hardly obtained those having satisfactory affinity with organism.
As described above, various problems still reside in both the conventional artificial bone and the conventional artificial tooth root (dental root).
In dentistry for treating teeth having relatively similar organization to that of bones, an adhesive comprising 4-(2-methacryloyloxyethyl)trimellitic anhydride (referred to hereinafter as "4-META") or hydrolyzate thereof (i.e., 4-(2-methacryloyloxyethyl)trimellitic acid, referred to hereinafter as "4-MET"), MMA and tri-n-butylborane (referred to hereinafter as "TBB") has been employed for adhering a metal crown to dentin.
The components of dentin are almost the same as those of a natural bone, so that the present inventors have tried to utilize the adhesion techniques of the dental art in the art of artificial bones. However, even if such techniques are utilized, an adhesive force of the adhesive tends to lower when the adhesive is immersed in water for a long period of time because the affinity of the adhesive with a natural bone is insufficient. For these reasons, it is difficult to firmly adhere an artificial bone to a natural bone without denaturing organization of the natural bone even by the use of the adhesion techniques of dentistry for burying the artificial bone.